U.S. patent number 6,630,970 [Application Number 09/897,318] was granted by the patent office on 2003-10-07 for polarizers for use with liquid crystal displays.
This patent grant is currently assigned to 3M Innovative Properties Company. Invention is credited to John C. Branca, John Cael, David M. Foresyth, James Gordon, William Pugh, Philip Ralli, William K. Smyth, Atsushi Suzuki, Giorgio Trapani.
United States Patent |
6,630,970 |
Trapani , et al. |
October 7, 2003 |
**Please see images for:
( Certificate of Correction ) ** |
Polarizers for use with liquid crystal displays
Abstract
A liquid crystal display structure includes a liquid crystal
display cell having a front surface and a back surface. One or more
intrinsic polarizers lacking protective coatings thereon, such as
K-type polarizers and thin KE polarizer sheets, are disposed
adjacent to the front and back surfaces of the liquid crystal
display cell. Alternatively, thinly cladded or encased iodine
polarizers are disposed adjacent to the front and back surfaces of
the liquid crystal display cell. The liquid crystal display
structure may be used in conjunction with other optical display
elements to enhance the brightness and contrast of the liquid
crystal display.
Inventors: |
Trapani; Giorgio (Cambridge,
MA), Smyth; William K. (Sudbury, MA), Ralli; Philip
(Sudbury, MA), Gordon; James (Newton, MA), Cael; John
(Upton, MA), Branca; John C. (Franklin, MA), Foresyth;
David M. (Plainville, MA), Suzuki; Atsushi (Westborough,
MA), Pugh; William (Naperville, IL) |
Assignee: |
3M Innovative Properties
Company (St. Paul, MN)
|
Family
ID: |
25407746 |
Appl.
No.: |
09/897,318 |
Filed: |
July 2, 2001 |
Current U.S.
Class: |
349/96;
359/487.06; 359/489.07; 359/493.01 |
Current CPC
Class: |
G02F
1/133528 (20130101) |
Current International
Class: |
G02F
1/13 (20060101); G02F 1/1335 (20060101); G01F
001/133 () |
Field of
Search: |
;349/96-103
;359/483 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
362275202 |
|
Nov 1987 |
|
JP |
|
10260395 |
|
Sep 1998 |
|
JP |
|
WO 00/65385 |
|
Nov 2000 |
|
WO |
|
WO 01/31393 |
|
May 2001 |
|
WO |
|
WO 02/10845 |
|
Feb 2002 |
|
WO |
|
Other References
Plastics In Flat Panel Displays (XP-001094690), Polaroid
Corporation, Cambridge, MA Joseph DelPico, Program Manager--Flat
Panel Displays; Giorgio Trapani, Chief Scientist--Polarizer
Division; John Branca, Director of Research--Holographic Division.
No. 150, Apr. 29-30, 1998, pp. 105-110. Germany. .
John J. Cael et al., High Durability KE Polarizers for LCD
Applications, Polaroid Corporation pp. 1-5, copyright 1995,
document dated Jul. 26, 2000..
|
Primary Examiner: Dudek; James
Attorney, Agent or Firm: Kirkpatrick & Lockhart LLP
Claims
What is claimed is:
1. A liquid crystal display structure comprising: a liquid crystal
display cell having a front surface and a back surface; and a front
intrinsic polarizer disposed adjacent to the front surface of the
liquid crystal display cell, the front intrinsic polarizer lacking
a protective coating thereon and providing a moisture vapor
transmission rate of less than about 4.6 gm/m.sup.2 /day and an
oxygen transmission rate of less than about 0.005 ml/m.sup.2 /day
to the liquid crystal display structure.
2. The liquid crystal display structure of claim 1, further
comprising a back intrinsic polarizer disposed adjacent to the back
surface of the liquid crystal display cell, the back intrinsic
polarizer lacking a protective coating thereon.
3. The liquid crystal display structure of claim 1, wherein the
front intrinsic polarizer is a K-type polarizer.
4. The liquid crystal display structure of claim 1, wherein the
front intrinsic polarizer comprises a KE polarizer sheet.
5. The liquid crystal display structure of claim 1, wherein the
front intrinsic polarizer has a first surface disposed adjacent to
the front surface of the liquid crystal display cell, the liquid
crystal display structure further comprising an adhesive layer
disposed on the first surface of the front intrinsic polarizer to
attach the intrinsic polarizer to the liquid crystal display
cell.
6. The liquid crystal display structure of claim 5, wherein the
adhesive layer comprises a pressure sensitive adhesive.
7. The liquid crystal display structure of claim 6, wherein the
adhesive layer comprises a diffuse adhesive.
8. The liquid crystal display structure of claim 1, further
comprising a removable release liner disposed adjacent to the front
intrinsic polarizer.
9. The liquid crystal display structure of claim 1, further
comprising a polyethylene terephthalate support layer disposed
adjacent to the front intrinsic polarizer.
10. The liquid crystal display structure of claim 1, further
comprising a transflective coating disposed adjacent to the back
intrinsic polarizer.
11. The liquid crystal display structure of claim 2, further
comprising a retarder disposed adjacent to the front intrinsic
polarizer.
12. The liquid crystal display structure of claim 2, further
comprising a liquid crystal polymer coating disposed adjacent to
the front intrinsic polarizer.
13. The liquid crystal display structure of claim 1, further
comprising a transflector disposed adjacent to the back intrinsic
polarizer.
14. The liquid crystal display structure of claim 13, wherein the
transflector comprises a layer of metal.
15. The liquid crystal display structure of claim 13, wherein the
transflector comprises a tilted mirror film.
16. The liquid crystal display structure of claim 13, wherein the
transflector comprises a holographic element.
17. The liquid crystal display structure of claim 2, wherein the
back intrinsic polarizer has a first surface disposed adjacent to
the back surface of the liquid crystal display cell and a second
surface, the liquid crystal display structure further comprising a
microreplicated structure formed on the second surface of the back
intrinsic polarizer.
18. The liquid crystal display structure of claim 2, further
comprising a reflective diffuse polarizer film adjacent to the back
intrinsic polarizer.
19. A liquid crystal display structure comprising: a liquid crystal
display cell having a front surface; an intrinsic polarizer having
a first surface disposed adjacent to the front surface of the
liquid crystal display cell and a second surface, the intrinsic
polarizer lacking a protective coating thereon and providing a
moisture vapor transmission rate of less than about 4.6 gm/m.sup.2
/day and an oxygen transmission rate of less than about 0.005
ml/m.sup.2 /day to the liquid crystal display structure; and a
conductor disposed adjacent to the second surface of the intrinsic
polarizer.
20. The liquid crystal display structure of claim 19, wherein the
intrinsic polarizer is a K-type polarizer.
21. A liquid crystal display structure comprising: a liquid crystal
display cell having a front surface and a back surface; a front
K-type polarizer disposed adjacent to the front surface of the
liquid crystal display cell, the front K-type polarizer lacking a
protective coating thereon and providing a moisture vapor
transmission rate of less than about 4.6 gm/m.sup.2 /day and an
oxygen transmission rate of less than about 0.005 ml/m.sup.2 /day
to the liquid crystal display structure; and a back K-type
polarizer disposed adjacent to the back surface of the liquid
crystal display cell, the back K-type polarizer lacking a
protective coating thereon.
22. An optical system comprising: a liquid crystal display
structure providing a moisture vapor transmission rate of less than
about 4.6 gm/m.sup.2 /day and an oxygen transmission rate of less
than about 0.005 ml/m.sup.2 /day, the liquid crystal display
structure comprising a liquid crystal display cell having a front
surface and a back surface and a front intrinsic polarizer disposed
adjacent to the front surface of the liquid crystal display cell,
the front intrinsic polarizer lacking a protective coating
thereon.
23. The optical system of claim 22 wherein the liquid crystal
display structure further comprises a back intrinsic polarizer
disposed adjacent to the back surface of the liquid crystal display
cell, the back intrinsic polarizer lacking a protective coating
thereon.
Description
TECHNICAL FIELD
This invention relates to liquid crystal displays, and more
particularly to polarizers for use with liquid crystal
displays.
BACKGROUND
Liquid crystal displays are optical displays used in devices such
as laptop computers, hand-held calculators and digital watches. A
typical liquid crystal display includes a liquid crystal display
cell and an electrode matrix disposed between a pair of absorbing
polarizers. The liquid crystal display cell contains, e.g., twisted
nematic or super twisted nematic molecules. In the liquid crystal
display, the optical state of portions of the liquid crystal
display cell is altered by the application of an electric field
using the electrode matrix. This creates an optical contrast for
light passing through the liquid crystal display cell that results
in the appearance of pixels of polarized light on the liquid
crystal display.
A typical liquid crystal display includes a front polarizer and a
rear polarizer. These polarizers may be plane polarizers that
absorb light of one polarization orientation more strongly than
they absorb light of the orthogonal polarization orientation. The
transmission axis of the front polarizer is usually crossed with
the transmission axis of the rear polarizer in a liquid crystal
display. The angle by which these transmission axes are crossed can
vary from zero degrees to ninety degrees.
In general, unpolarized ambient light waves vibrate in a large
number of directions without having a single characterizing
electromagnetic radiation vector. By contrast, plane polarized
light consists of light waves having a direction of vibration along
a single electromagnetic radiation vector. Also, circularly
polarized light has a direction of vibration along an
electromagnetic radiation vector that rotates as the light
propagates through space. Polarized light has many applications in
electro-optical devices, such as the use of plane and circular
polarizing filters to reduce glare in displays.
Further, much commercial attention has been directed to the
development and improvement of flat panel displays, particularly
thin, compact flat panel displays. A problem encountered in the
construction of plastic flat panel displays is the development of
"black spots," which arise from the formation of bubbles in the
liquid crystal material from gas that has permeated through the
plastic display materials. Another problem associated with plastic
flat panel displays is moisture contamination of the liquid crystal
display cell. These problems are avoided in conventional liquid
crystal displays by using low permeability glass substrates instead
of plastic. With respect to plastic flat panel displays, these
problems are addressed by adding additional gas and moisture
barrier layers to the liquid crystal display structure and/or the
plastic substrates. However, adding such gas and moisture barrier
layers increases the thickness, weight and cost of the
displays.
Polarizers in the form of synthetic polarizing films exhibit
comparative ease of manufacture and handling and comparative ease
with which they may be incorporated into electro-optical devices
such as flat panel displays. In general, plane polarizing films
have the property of selectively passing radiation vibrating along
a given electromagnetic radiation vector and absorbing
electromagnetic radiation vibrating along a second electromagnetic
radiation vector based on the anisotropic character of the
transmitting film medium. Plane polarizing films include dichroic
polarizers, which are absorbing plane polarizers utilizing the
vectorial anisotropy of their absorption of incident light waves.
The term "dichroism" refers to the property of differential
absorption of the components of incident light, depending on the
vibration directions of the component light waves. Light entering a
dichroic plane polarizing film encounters two different absorption
coefficients along transverse planes, one coefficient being high
and the other coefficient being low. Light emerging from a dichroic
film vibrates predominantly in the plane characterized by the low
absorption coefficient.
Dichroic plane polarizing films include H-type (iodine) polarizers
and dyestuff polarizers. For example, an H-type polarizer is a
synthetic dichroic sheet polarizer including a polyvinyl
alcohol-iodine complex. Such a chemical complex is referred to as a
chromophore. The base material of an H-type polarizer is a
water-soluble high molecular weight substance, and the resulting
film has relatively low moisture and heat resistance and tends to
curl, peel or otherwise warp when exposed to ambient atmospheric
conditions. Further, H-type polarizers are inherently unstable, and
require protective cladding, e.g., layers of cellulose triacetate,
on both sides of the polarizer to prevent degradation of the
polarizer in a normal working environment such as in a liquid
crystal display.
In contrast to H-type polarizers and other similar synthetic
dichroic plane polarizers are intrinsic polarizers and thinly
cladded or encapsulated polarizers. Intrinsic polarizers polarize
light due to the inherent chemical structure of the base material
used to form the polarizer. Such intrinsic polarizers are also
typically thin and durable. Examples of intrinsic polarizers are
K-type polarizers. A thinly cladded or encapsulated polarizer may
be, e.g., an iodine polarizer coated on both surface with polymer
coatings each having a thickness of only about 5 microns, and is
also thin and durable.
A K-type polarizer is a synthetic dichroic plane polarizer based on
molecularly oriented polyvinyl alcohol (PVA) sheets or films with a
balanced concentration of light-absorbing chromophores. A K-type
polarizer derives its dichroism from the light absorbing properties
of its matrix, not from the light-absorbing properties of dye
additives, stains, or suspended crystalline materials. Thus, a
K-type polarizer may have both good polarizing efficiency and good
heat and moisture resistance. A K-type polarizer may also be very
neutral with respect to color.
An improved K-type polarizer, referred to as a KE polarizer, is
manufactured by 3M Company, Norwood, Mass. The KE polarizer has
improved polarizer stability under severe environmental conditions,
such as high temperatures and high humidity. In contrast to H-type
polarizers, in which the light absorption properties are due to the
formation of a chromophore between PVA and tri-iodide ion, KE
polarizers are made by chemically reacting the PVA by an acid
catalyzed, thermal dehydration reaction. The resulting chromophore,
referred to as polyvinylene, and the resulting polymer may be
referred to as a block copolymer of vinylalcohol and vinylene.
For H-type polarizers, stability is achieved by sandwiching the
polarizer between two plastic substrates, such as two layers of
cellulose triacetate, one on each side of the polarizer. However,
even in these structures the application of heat, humidity and/or
vacuum can adversely affect the properties of the polarizer. By
contrast, K-type polarizers such as KE polarizers do not need to be
sandwiched between sheets of cellulose triacetate. The polyvinylene
chromophore of the KE polarizer is an extremely stable chemical
entity, since the chromophore is intrinsic to the polymer molecule.
This chromophore is thermally stable as well as resistant to attack
from a wide range of solvents and chemicals.
A K-type polarizer such as a KE polarizer has several advantages
over other types of polarizers, e.g., iodine and dyestuff
polarizers. K-type polarizers have more durable chromophores, are
thinner, and may be designed with variable transmission levels.
Most notably, K-type polarizers such as KE polarizers may be used
in applications that require high performance under severe
environmental conditions, including high temperatures and high
humidity, such as 85.degree. C. and 85% relative humidity, for
extended periods of time. Under such extreme environmental
conditions, the stability of iodine polarizers is greatly reduced,
thus limiting their usefulness in applications such as flat panel
displays. Due to the inherent chemical stability of K-type
polarizers, a wide variety of adhesive formulations, including
pressure sensitive adhesives, can be applied directly to K-type
polarizers. Further, a single-sided plastic support is adequate to
give physical support for K-type polarizers, and since this support
can be located outside the optical path of the liquid crystal
display module, it need not be optically isotropic and lower-cost
substrates such as polyethylene terephthalate (PET) are acceptable
alternatives. Moreover, the ability to construct single-sided
laminates allows the optical structures to be thinner, allowing for
additional flexibility in the design and manufacture of flat panel
display elements. These advantages of K-type polarizers may be used
in a wide variety of optical applications, including flat panel
displays.
In contrast to a plane polarizer, a circular polarizer may be
constructed of a plane polarizer and a quarter-wavelength retarder.
A quarter-wavelength retarder shifts the phase of light waves
propagating along one plane through the retarder by one-quarter
wavelength, but does not shift the phase of light waves propagating
through the retarder along a transverse plane. The result of
combining light waves that are one-quarter wavelength out of phase
and that vibrate along perpendicular planes is circularly polarized
light, for which the electromagnetic radiation vector rotates as
the combined light waves travel through space.
Circularly polarized light may be described with respect to two
distinct polarization states: left-handed (L) and right-handed (R)
circularly polarized light. A circular polarizer absorbs light of
one of these polarization states and transmits light of the other
polarization state. The use of circular polarizers to reduce glare
in displays is well known. In particular, light from an emissive
display can be selectively transmitted through a circular
polarizer, while background ambient light reflected in the display,
which causes glare, may be reduced or eliminated.
A conventional liquid crystal display stack 10 is shown in FIG. 1.
A liquid crystal display cell 12 has two surfaces coated with
layers 14, 16 of an adhesive, e.g., a pressure sensitive adhesive,
to secure polarizer structures to both surfaces of the liquid
crystal display cell. The polarizer structures each include plane
polarizers 18, 20, e.g., H-type polarizers, which have layers 22,
24, 26, 28 of cellulose triacetate as a protective cladding coated
or laminated on both surfaces thereof. Liquid crystal display stack
10 also typically includes a transflector or reflector 30 attached
to the back side of the display by an adhesive layer 32, e.g., a
pressure sensitive adhesive, the transflector or reflector
functioning to enhance the brightness and contrast of the liquid
crystal display. H-type polarizers 18, 20 each typically have a
thickness of approximately 20 microns, each of the layers of
cellulose triacetate 22, 24, 26, 28 is typically approximately 80
microns thick, and pressure sensitive adhesive layer 32 typically
has a thickness of approximately 25 microns.
SUMMARY
In general, in one aspect, the invention features a liquid crystal
display structure including a liquid crystal display cell having a
front surface and a back surface. A front intrinsic polarizer is
disposed adjacent to the front surface of the liquid crystal
display cell, the front intrinsic polarizer lacking a protective
coating thereon.
Implementations of the invention may also include one or more of
the following features. The liquid crystal display structure may
include a back intrinsic polarizer disposed adjacent to the back
surface of the liquid crystal display cell, the back intrinsic
polarizer lacking a protective coating thereon.
The front intrinsic polarizer may be a K-type polarizer, a KE
polarizer sheet, or a thin film. The front intrinsic polarizer has
a first surface disposed adjacent to the front surface of the
liquid crystal display cell, the liquid crystal display structure
further including an adhesive layer disposed on the first surface
of the front intrinsic polarizer to attach the intrinsic polarizer
to the liquid crystal display cell.
The adhesive layer may include a pressure sensitive adhesive or a
diffuse adhesive. The liquid crystal display structure may include
a removable release liner disposed adjacent to the front intrinsic
polarizer. The liquid crystal display structure may include a
polyethylene terephthalate support layer disposed adjacent to the
front intrinsic polarizer.
The liquid crystal display structure may include a transflective
coating disposed adjacent to the back intrinsic polarizer. The
liquid crystal display structure may include a retarder or a liquid
crystal polymer coating disposed adjacent to the front intrinsic
polarizer.
The liquid crystal display structure may include a transflector
disposed adjacent to the back intrinsic polarizer. The transflector
may include a layer of metal, a tilted mirror film, or a
holographic element. The back intrinsic polarizer may have a first
surface disposed adjacent to the back surface of the liquid crystal
display cell and a second surface, the liquid crystal display
structure further including a microreplicated structure formed on
the second surface of the back intrinsic polarizer. The liquid
crystal display structure may include a reflective diffuse
polarizer film disposed adjacent to the back intrinsic
polarizer.
In general, in another aspect, the invention features a liquid
crystal display structure including a liquid crystal display cell
having a first surface. An intrinsic polarizer has a first surface
disposed adjacent to the front surface of the liquid crystal
display cell and a second surface, the intrinsic polarizer lacking
a protective coating thereon. A conductor is disposed adjacent to
the second surface of the intrinsic polarizer.
Implementations of the invention may also include the following
feature. The intrinsic polarizer may be a K-type polarizer.
In general, in another aspect, the invention features a liquid
crystal display structure, including a liquid crystal display cell
having a front surface and a back surface. A front K-type polarizer
is disposed adjacent to the front surface of the liquid crystal
display cell, the front K-type polarizer lacking a protective
coating thereon. A back K-type polarizer is disposed adjacent to
the back surface of the liquid crystal display cell, the back
K-type polarizer lacking a protective coating thereon.
In general, in another aspect, the invention features a liquid
crystal display structure including a liquid crystal display cell
having a front surface and a back surface. A front thinly cladded
iodine polarizer is disposed adjacent to the front surface of the
liquid crystal display cell, the front thinly cladded iodine
polarizer lacking a protective coating thereon.
Implementations of the invention may also include the following
feature. The liquid crystal display structure may include a back
thinly cladded iodine polarizer disposed adjacent to the back
surface of the liquid crystal display cell, the back thinly cladded
iodine polarizer lacking a protective coating thereon.
An advantage of the present invention is elimination of the need
for protective cladding of the polarizers in the liquid crystal
display stack, resulting in significant reduction in the thickness
of the liquid crystal display. Thus, an additional advantage of the
invention is the ability to manufacture thinner and lighter-weight
liquid crystal displays. Another advantage of the present invention
is that an intrinsic polarizer such as a K-type polarizer provides
stable performance over a wide range of transmission levels. A
further advantage of the present invention is increased brightness
of liquid crystal displays using K-type polarizers compared to
currently manufactured liquid crystal displays, with resulting
lower energy requirements for illumination of the display.
The details of one or more embodiments of the invention are set
forth in the accompanying drawings and the description below. Other
features, objects, and advantages of the invention will be apparent
from the description and drawings, and from the claims.
DESCRIPTION OF DRAWINGS
FIG. 1 is a cross sectional view of a conventional liquid crystal
display stack.
FIG. 2 is a cross sectional view of a liquid crystal display stack
according to the present invention.
FIG. 3 is a cross sectional view of an alternative polarizer
structure that may be attached to the back side of a liquid crystal
display device.
FIG. 4 is a cross sectional view of an alternative polarizer
structure to that shown in FIG. 3.
FIG. 5 is a cross sectional view of another alternative polarizer
structure to that shown in FIG. 4.
FIG. 6 is a cross sectional view of an alternative polarizer
structure that may be attached to the viewing side of a liquid
crystal device.
FIG. 7 is a cross sectional view of a liquid crystal display module
with a circular polarizer.
FIG. 8 is a cross sectional view of an alternative polarizer
structure to that shown in FIG. 6.
FIG. 9 is a cross sectional view of another alternative polarizer
structure to that shown in FIG. 6.
FIG. 10 is a cross sectional view of an alternative polarizer
structure that may be attached to the back side of a liquid crystal
device.
FIG. 11 is a cross sectional view of another alternative polarizer
structure that may be attached to the back side of a liquid crystal
device.
FIG. 12 is a cross sectional view of polarizer structure that can
be attached to the back side of a liquid crystal device that is an
alternative to the polarizer structures of FIGS. 10 and 11.
FIG. 13 is a cross sectional view of a polarizer structure using an
intrinsic polarizer as a substrate for a conductor in a liquid
crystal display.
FIGS. 14A-14C are cross sectional views of a polarizer structure
being formed using an intrinsic polarizer as a substrate for a
microreplicated structure.
FIG. 15 is a cross sectional view of a polarizer structure using an
intrinsic polarizer attached to a reflective diffuse polarizer
film.
Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
The present invention relates to the use of intrinsic polarizers
disposed adjacent to either the front surface or the rear surface,
or both, of a liquid crystal display cell. Alternatively, thinly
cladded or encased iodine polarizers may be disposed adjacent to
either or both surfaces of a liquid crystal display cell.
FIG. 2 shows a liquid crystal display stack 50 according to the
present invention. A liquid crystal display cell 52 is coated with
layers 54, 56 of an adhesive, e.g., a pressure sensitive adhesive
such as Polatechno AD-20, to secure polarizer structures to the
liquid crystal display cell, similar to liquid crystal display
stack 10 shown in FIG. 1. On the viewing side of liquid crystal
display stack 50, an intrinsic polarizer 58, preferably a K-type or
thin KE polarizer sheet, is attached to liquid crystal display cell
52 using adhesive layer 56. K-type polarizer 58 typically has a
thickness of approximately 20 microns. Such a KE polarizer may be a
sheet of the type manufactured by 3M Company, Norwood, Mass. K-type
polarizer 58 may also include a supporting substrate in the form of
a polyethylene terephthalate (PET) support layer 60 on its surface
facing the viewing side of the liquid crystal display. PET support
layer 60 typically has a thickness of approximately 25-180 microns.
However, liquid crystal display stack 50 does not require a
supporting substrate such as PET support layer 60; for example, a
KE polarizer sheet may itself be attached to a display.
On the back side of liquid crystal display stack 50, another
intrinsic polarizer 62 such as a K-type or thin KE polarizer sheet
is attached to liquid crystal display cell 52 using adhesive layer
54. K-type polarizer 62 also typically has a thickness of
approximately 20 microns. A transflector or reflector 64 may be
disposed on the surface of K-type polarizer 62 facing the back side
of the liquid crystal display to enhance the brightness and
contrast of the liquid crystal display.
Using intrinsic polarizers in the liquid crystal display stack
eliminates the need for protective cladding of the polarizers. The
cladding used for other types of polarizers, e.g., H-type
polarizers, is generally a layer of cellulose triacetate disposed
on both sides of the polarizer. Removing the cladding layers of
cellulose triacetate results in a significant reduction in the
thickness of the liquid crystal display stack. For example, liquid
crystal display stack 50 of FIG. 2, including PET support layer 60
and transflector or reflector 64, is approximately 300 microns
thinner than the corresponding liquid crystal display stack 10 of
FIG. 1.
Further, the K-type polarizers used in liquid crystal display stack
50 could provide an effective gas and moisture permeability barrier
to the liquid crystal material in the liquid crystal display cell.
Thus, no additional barrier layers or cladding may be needed in a
liquid crystal display structure constructed with a K-type
polarizer disposed on each side of the liquid crystal display cell
to achieve desired permeability specifications. In particular, a
standard for moisture vapor transmission rate (MVTR), ASTM F1249,
is less than 20 gm/m.sup.2 /day, and the oxygen transmission rate
(O2GTR), ASTM D3985, is less than 1 ml/m.sup.2 /day. Structures for
liquid crystal displays formed using KE polarizers, including PET
support structures, have been shown to have a MVTR of 4.6 or less
gm/m2/day and an O2GTR of less than 0.005 ml/m.sup.2 /day (tested
at 20.degree. C. and 90% relative humidity).
Although the present description refers to intrinsic polarizers,
thinly cladded or encased iodine polarizer may be substituted for
either or both intrinsic polarizers. A thinly cladded polarizer
includes an iodine polarizer sheet coated on both surfaces with
polymer coatings each having a thickness of about 5 microns. A
thinly cladded polarizer is thin and durable, similar to an
intrinsic polarizer such as a K-type polarizer.
FIG. 3 shows an alternative polarizer structure 80 that may be
attached to the back side of a liquid crystal display device. An
intrinsic polarizer 82 such as a K-type or thin KE polarizer sheet
may have an adhesive layer 84, e.g., a pressure sensitive adhesive,
on one of its surfaces, which adhesive layer is covered by a
removable release liner 86 prior to attaching polarizer structure
80 to the liquid crystal display. For example, the typical
thickness of KE polarizer 82 is approximately 15-35 microns, the
typical thickness of pressure sensitive adhesive coating 84 is
approximately 16-35 microns, and the typical thickness of release
liner 86 is approximately 25-50 microns. Further, KE polarizer 82
may be laminated onto release liner 86 having pressure sensitive
adhesive coating 84 previously applied thereon. A PET support layer
88 having a transflective coating 90 may be attached to the other
surface of intrinsic polarizer 82 by an adhesive layer 92. Since
one surface of a KE polarizer sheet typically comprises a PET
layer, an adhesive other than a pressure sensitive adhesive may be
used, e.g., a coated adhesive that is thermally cured such as a
copolyester adhesive that is crosslinked using multifunctional
isocyanates. Transflective coating 90 functions to enhance the
brightness and contrast of the liquid crystal display.
Transflective coating 90, which typically has a thickness of
approximately 8-20 microns, may be coated on or laminated onto PET
support layer 88. The transflective coating may be, e.g., a
nacreous pigment coated onto PET such as commercially available
STR400 from Nippon Paper or a transflector available from Teijin.
The typical thickness of adhesive layer 92 is approximately 4-20
microns, and the typical thickness of PET support layer 88 is
approximately 12-100 microns.
FIG. 4 shows an alternative polarizer structure 94 to that shown in
FIG. 3. Polarizer structure 94 includes no PET support layer.
Instead, transflective coating 90 may be contained on or laminated
onto intrinsic polarizer 82, which may have an adhesive layer 95,
e.g., having a thickness up to approximately 20 microns, or no
adhesive layer at all.
FIG. 5 shows another alternative polarizer structure 96 to that
shown in FIG. 3. Polarizer structure 96 has a PET support layer 88
attached to intrinsic polarizer 82 by a diffuse adhesive layer 98.
Diffuse adhesive 98, which typically has a thickness of
approximately 12-40 microns, functions similarly to the combination
of an adhesive layer and a transflective coating to enhance the
brightness of the liquid crystal display and to attach PET support
layer 88 to intrinsic polarizer 82. For example, diffuse adhesive
98 may be a pressure sensitive adhesive to which glass beads have
been added to scatter light passing through the adhesive.
FIG. 6 shows an alternative polarizer structure 100 that may be
attached to the front surface of a liquid crystal device. A
retarder 102 such as a quarter-wavelength retarder has an adhesive
layer 104, e.g., a pressure sensitive adhesive, on one of its
surfaces, which adhesive layer is covered by a removable release
liner 107 prior to attaching polarizer structure 100 to the liquid
crystal display. Retarder 102 is preferably a thin film, broadband
quarter-wavelength retarder effective over all or a substantial
portion of the visible electromagnetic spectrum, such as the
broadband quarter-wavelength retarders manufactured by Teijin. For
example, the typical thickness of quarter-wavelength retarder 102
is approximately 30-60 microns, the typical thickness of pressure
sensitive layer 104 is approximately 16-35 microns, and the typical
thickness of release liner 107 is approximately 25-50 microns.
An intrinsic polarizer 106 such as a K-type or thin KE polarizer
sheet has an adhesive layer 108, on one of its surfaces, which
adhesive layer is attached to the other surface of retarder 102.
The typical thickness of KE polarizer 106 is approximately 15-35
microns, and the typical thickness of adhesive layer 108 is
approximately 5-30 microns.
A PET support layer 110 having an antireflective coating 112 may be
attached to the other surface of intrinsic polarizer 106 by an
adhesive layer 114. Antireflective coating 112, which typically has
a thickness of less than 1 micron, may be made from a low index of
refraction thermopolymer such as Kynar 1702 and may be coated on
one surface of PET support layer 110. The typical thickness of
adhesive layer 92 on the other surface of PET support layer 110 is
approximately 5-30 microns, and the typical thickness of PET
support layer 110 itself is approximately 12-100 microns.
The combination of intrinsic polarizer 106 with retarder 102 acts
as a circular polarizer, which significantly reduces the intensity
of undesirable reflected ambient light, thereby increasing the
contrast of the image formed by the emitted signal from the
display. As shown in FIG. 7, unpolarized ambient light 202 may be
represented as a combination of left-handed (L) 204 and
right-handed (R) 206 circularly polarized light components. When
unpolarized ambient light 202 enters liquid crystal display 200,
one circularly polarized component of the ambient light, e.g.,
left-handed circular polarized light 204, is absorbed by the
combination of polarizer 106 with retarder 102, while the other
component, the right-handed circularly polarized light 206, is
transmitted through the liquid crystal display. The transmitted
right-handed circularly polarized light 206 is specularly reflected
in the liquid crystal display. However, the handedness of
circularly polarized light is reversed upon specular reflection,
and the transmitted right-handed circularly polarized light 206
becomes left-handed circularly polarized light. The reflected
left-handed circularly polarized light is reflected toward the
combination of polarizer 106 with retarder 102, where it is
absorbed in the same manner as the left-handed circularly polarized
component 204 of ambient light 202. Thus, both the left-handed and
right-handed circularly polarized components of the ambient light
are absorbed by the combination of polarizer 106 and retarder 102,
which acts as a circular polarizer, during transmission through and
reflection in liquid crystal display 200 so that they do not
interfere with an emitted light signal 210.
FIG. 8 shows an alternative polarizer structure 120 to that shown
in FIG. 6. Polarizer structure 120 includes no PET support layer.
Instead, antireflective coating 112 or alternatively a hard coat
113 may be coated on or laminated onto intrinsic polarizer 106.
Hard coat 113, which typically has a thickness of 1-6 microns, may
be made, e.g., from an acrylate such as poly methyl methacrylate.
Hard coat 113 may be either matte or clear.
FIG. 9 shows another alternative polarizer structure 130 to that
shown in FIG. 6. In polarizer structure 130, retarder 102 and
adhesive layer 108 are replaced by a liquid crystal polymer coating
132 disposed on intrinsic polarizer 106. Liquid crystal polymer
coating 132, which typically has a thickness of up to approximately
100 microns, performs the function of enhancing the thickness of
the liquid crystal display similar to retarder 102 of FIG. 6.
FIG. 10 shows an alternative polarizer structure 140 with enhanced
brightness that may be attached to the back side of a liquid
crystal device. In polarizer structure 140, a holographic element
transflector known as Light Intensifying Film Technology (LIFT) 142
is laminated to an intrinsic polarizer 144 such as a K-type or thin
KE polarizer sheet. As set forth in U.S. Pat. No. 5,886,799, LIFT
includes a micro replicated structure 146 metalized with a layer of
aluminum 148 that is formed on a PET support layer 150. The
microreplicated surface of LIFT layer 142 may be attached to one
surface of intrinsic polarizer 144 with an adhesive layer 152,
e.g., a pressure sensitive adhesive. A release liner 154 may be
attached to the other surface of intrinsic polarizer 144 by another
adhesive layer 156, e.g., a pressure sensitive adhesive. LIFT layer
142 enhances the brightness of the liquid crystal display by
directing light transmitted through the liquid crystal display
toward a region normal to the display's surface.
FIG. 11 shows another alternative polarizer structure 160 with
enhanced brightness that may be attached to the back side of a
liquid crystal device. In polarizer structure 160, a transflector
known as Tilted Mirror Film (TMF) 162 is laminated to an intrinsic
polarizer 164 such as a K-type or thin KE polarizer sheet. TMF 162
includes a microreplicated structure 166 metalized with a layer of
silver 168 that is formed on a PET support layer 170. The
microreplicated surface of TMF layer 162 may be attached to one
surface of K-type polarizer 164 with an adhesive layer 172, e.g.,
an optically clear pressure sensitive adhesive. A release liner 174
may be attached to the other surface of K-type polarizer 164 by
another adhesive layer 176, e.g., an optically clear pressure
sensitive adhesive. Alternatively, either adhesive layer 172 or
adhesive layer 176 may be a diffuse pressure sensitive adhesive
that diffusely scatters light.
FIG. 12 shows a polarizer structure 180 with enhanced brightness
that can be attached to the back side of a liquid crystal device
that is an alternative to the polarizer structures of FIGS. 10 and
11. In particular, a simple transflector 182 in the form of a layer
of metal such as silver or aluminum applied directly to one surface
of an intrinsic polarizer 184 acts as a polarized mirror to reflect
polarized light and enhance the brightness of the liquid crystal
display. Transflector 182 may be formed by sputtering, vacuum
depositing, or otherwise coating a layer of silver or aluminum to
K-type polarizer 184. Another example of a transflector is a
coating of mica on a polymer or adhesive matrix.
The use of a non-depolarizing, diffuse pressure sensitive adhesive
layer 186 to attach a release liner 188 to intrinsic polarizer 184
further diffuses polarized light to enhance the brightness of the
liquid crystal display. Alternatively, for a silver transflector
182, a PET support layer 190 may be attached to the transflector by
an adhesive layer 192, e.g., a pressure sensitive adhesive. As an
additional alternative, silver transflector 182 may be disposed on
a non-birefringent carrier (not shown) attached to K-type polarizer
184. Such a non-birefringent carrier may be, e.g., cellulose
triacetate, a diacetate, or Transphan.
FIG. 13 shows a polarizer structure 300 using an intrinsic
polarizer as a substrate for a conductor in a liquid crystal
display without requiring any adhesive. In polarizer structure 300,
a conductor 302 in the form of a metal layer 304, e.g., aluminum,
disposed between layers of indium tin oxide (ITO) 306, 308 is
attached to a hard coat 310 deposited or coated directly onto
K-type polarizer 312. A conductor pattern may then be etched into
layers 304, 306, 308 of conductor 302.
FIGS. 14A-14C show how a polarizer structure 320 may be formed
using an intrinsic polarizer as a substrate for a microreplicated
structure. FIG. 14A shows an intrinsic polarizer 322, e.g., a
K-type or thin KE polarizer sheet, having a carrier or support
layer 324 attached by an adhesive (not shown). Carrier layer 324 is
not required to use intrinsic polarizer 322 as a substrate for a
microreplicated structure. In FIG. 14B, a layer of an
ultraviolet-curable resin 326 is disposed on the surface of
intrinsic polarizer 322 opposite to the surface attached to carrier
layer 324. Prior to curing resin 326, a microreplicating tool 328
is applied to resin 326 to form a microreplicated structure 330
(FIG. 14C). With tool 328 applied to the resin, resin 326 is then
cured to set the microreplicated structure, and then tool 328 is
removed. Microreplicated structure 330 enhances the brightness of
the liquid crystal display by directing light transmitted through
the liquid crystal display toward a region normal to the display's
surface.
FIG. 15 shows an alternative polarizer structure 400 that may be
attached to the rear surface of a liquid crystal display device. A
reflective diffuse polarizer film 402 is a multilayer polymer film
that functions as a reflective polarizer, i.e., as a white,
non-inverting filter than enhances the appearance of the liquid
crystal display. Reflective diffuse polarizer film 402 may be
attached to intrinsic polarizer 106 with an adhesive layer 114.
Reflective diffuse polarizer film 402 may also be a specular
reflective polarizer with a diffuse adhesive or a diffuse
reflective polarizer with a clear adhesive.
A number of embodiments of the invention have been described.
Nevertheless, it will be understood that various modifications may
be made without departing from the spirit and scope of the
invention. Accordingly, other embodiments are within the scope of
the following claims.
* * * * *